The association of cancer regression in patients undergoing bacterial infection was observed and reported at least as early as 1868. The systemic administration of live attenuated Salmonella organisms to solid tumor bearing animals was reported to result in tumor therapy. See, e.g., U.S. Pat. No. 6,685,935 and Pawelek et al., (Lancet Oncol. 4(9):548-56, 2003). Also, intravesical (non-systemic) administration of attenuated Gram-positive mycobacteria (BCG) is approved in the United States for the treatment and prophylaxis of carcinoma in situ (CIS) of the urinary bladder.
Improvements in tumor therapy using live Gram-negative Salmonella have also been reported for certain auxotrophic mutants. See e.g., Hoffman et al., (Amino Acids 37:509-521, 2009, U.S. Patent publication 20090300779 (Zhao et al.), and Zhao et al. (Proc. Natl. Acad. Sci. (USA) 102(3):775-760, 2005).
Salmonella having deletions in the msbB locus have been prepared which express LPS lacking terminal myristoylation of lipid A in the outer membrane. TNF-alpha induction in mice and swine treated with these msbB-Salmonella strains was 33% and 14% of the amount induced by wild-type bacteria, respectively. See e.g., Low et al., Nature 17:37-41, 1999 and U.S. Pat. No. 7,354,592 (Bermudes et al.). Administration of such live organisms, including strain VNP20009, has been reported to inhibit the growth of subcutaneously implanted B16F10 murine melanoma, and the human tumor xenografts Lox, DLD-1, A549, WiDr, HTB177, and MDA-MB-231 grown in mice (Luo et al., Oncol. Res. 12(11-12):501-508, 2001). Salmonella strain VNP20009 has also been reported to improve the anti-tumor efficacy of the chemotherapeutic agent cyclophosphamide at both a maximum tolerated dose and with a low-dose metronomic regimen (Jia et al., Int. J. Cancer 121(3):666-674, 2007).
Conditional mutants of Gram-negative bacteria that cannot produce Lipid A and that lack LPS in the outer membrane have been prepared but have been reported to be toxic to the organism. For example, mutational inhibition of synthesis of 3-deoxy-D-manno-octulosonate (Kdo) or mutational inhibition of incorporation of Kdo molecules into lipid IVA prevents lipid A and LPS synthesis and localization of LPS precursors to the outer membrane of Gram-negative bacteria. Lipid IVA is an LPS precursor that lacks glycosylation. Activation of these mutations leads to loss of bacterial viability (Rick et al., Proc. Natl. Acad. Sci. USA 69(12):3756-3760, 1972, Belunis et al. J. Biol. Chem. 270(46):27646-27652, 1995, and Taylor et al. J. Biol. Chem. 275(41):32141-32146, 2000).
It is also possible to inhibit Kdo incorporation into lipid IVA, synthesis of lipid A and localization to the outer membrane through the use of exogenously added compounds. Goldman et al. (J. Bacteriol. 170(5):2185-91, 1988) describe antibacterial agents that specifically inhibit CTP:CMP-3-deoxy-D-manno-octulosonate cytidylyltransferase activity, thereby blocking the incorporation of 2-keto 3-deoxy-D-manno-octulosonate (Kdo) into lipid IVA of Gram-negative organisms. As LPS synthesis ceased, molecules similar in structure to lipid IVA were found to accumulate, and bacterial growth ceased. The authors concluded that addition of Kdo to LPS precursor lipid species IVA is the major pathway of lipid A-Kdo2 formation in both S. typhimurium LT2 and Escherichia coli (E. coli).
More recently, mutants of Gram-negative bacteria have been prepared that lack LPS, including lipid A or 6-acyl lipidpolysaccharide, in the outer membrane but maintain viability. For example, U.S. Patent publication 2010/0272758 reports an E. coli K-12 strain KPM22 that is defective in synthesis of 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo). KPM22 has an outer membrane (OM) composed predominantly of lipid IVA. Viability of these organisms was achieved by the presence of a second-site suppressor that facilitates transport of lipid IVA from the inner membrane to the outer membrane. This suppressor is reported to relieve toxic side-effects of lipid IVA accumulation in the inner membrane and provide sufficient amounts of LPS precursors to support OM biogenesis. The LPS precursor produced by this strain lacks endotoxin activity, as determined by its inability to induce TNF-alpha secretion by human mononuclear cells at LPS precursor doses of up to 1 μg/mL. See also, Mamat et al., (Mol Microbiol. 67(3):633-48, 2008).
Dose-limiting side effects associated with infection and septic shock significantly limit systemic administration of live bacteria to cancer patients. This limitation has been associated with wildtype bacteria (see e.g., Wiemann and Starnes, Pharmac. Ther. 64:529-564, 1994 for review), and has also been associated with genetically attenuated bacteria, which proliferate selectively in tumor tissue and express modified lipid A (see e.g., Toso et al., J. Clin. Oncol. 20(1):142-152, 2002). These limitations have led to the use of heat killed bacteria for cancer therapy. See e.g., Havas et al. (Med. Oncol. & Tumour Pharmacother. 10(4):145-158, 1993), Ryoma et al. (Anticancer Res. 24:3295-3302, 2004), Maletzki et al. (Clin. Develop. Immunol. 2012:1-16, 2012), U.S. Pat. No. 8,034,359 B2 (Gunn), European Patent No. EP 1,765,391 B1 (Gunn), and for review, Wiemann and Starnes (Pharmac. Ther. 64:529-564, 1994). However, non-infectious, killed bacteria still induce significant dose-limiting toxicities associated with LPS-derived endotoxin and other cell constituents, which are pyrogenic and can produce symptoms of septic shock. Thus, further improvements in treating cancer with bacteria are needed.